The present invention relates to a method and apparatus for removing bead wire off from a wire spool with a bead making machine and more particularly to a method and apparatus for controlling the tension of the bead wire being fed off of the wire spool mounted in a bead wire letoff stand.
The tire building industry has been improving the methods and apparatus for controlling the tension of a wire or wires being fed into a bead making machine used in the manufacture of tire beads. The current practice is to place a roll or spool of wire in a device, commonly called a bead wire letoff stand, that allows the wire to be pulled from the spool at a controlled tension over a wide range of spool speeds (line speeds). The letoff stand must also be capable of stopping a full spool of wire at the maximum line speed. The control of the wire tension and the stopping of the rotating spool are typically accomplished with a braking device. One important consideration is that the latter mentioned functions of the braking device must be accomplished without allowing the mass of the spool to overcome the braking force of the braking device. Failure to overcome the inertia of the rotating mass would result in the spool of wire continuing to unwind. If the wire continues to unwind from the spool while not being used in the bead making machine, the wire will typically jump off the wire guide pulleys and accumulate as a heap of wire next to the let off stand.
In one current bead wire letoff stand, a somewhat complex mechanical linkage, includes a tension arm and linkage arms. A friction brake, mechanically connected to the tension arm, can apply a braking force to the wire spool depending upon the location of the tension arm. The pivot points in the tension arm and the associated linkage arms are prone to wear. Once the mechanical parts begin to wear, the letoff stand cannot maintain control of the tension of the wire being unwound from the wire spool and the stopping or slowing of the rotating wire spool as quickly and accurately as before the parts were at least somewhat worn. The mechanical linkage is adjustable by an operator so that the wire tension of the letoff stand can be held relatively constant irrespective of the mechanical wear. However, when a series of letoff stands are used in conjunction with each other to feed a plurality of bead wires a single bead forming device, each of the letoff stands typically exerts a somewhat different tension on the wire being unwound, as compared with the tension of a different one of the letoff stands. This variation in feed tension effects the winding tension of the beads, causing the formed wire beads to vary in inside diameter by several thousandths of an inch. This can result in an adverse effect on the quality and uniformity of the tire beads. In a worst case scenario, the tension varies enough to cause a problem known as xe2x80x9csplitout,xe2x80x9d or uncontrolled separation of the bead ribbon in the bead making apparatus, causing expensive downtime of the assembly procedure while the wires are restrung. Another important limiting design consideration of the current letoff stand designs is that they are generally limited to a wire line speed of about 250 fpm (feet per minute) [76.2 mpm (meters per minute)] to about 300 fpm [91.44 mpm]. New manufacturing methods require a faster line speed of at least about 500 fpm [152.4 mpm].
Accordingly, there is a need in the tire building industry for a letoff stand design that can effectively control the line tension and provide for braking of the wire spool.
It is an object of the present invention to provide a method and apparatus for controlling the tension of wire being pulled from a wire spool mounted on a bead wire letoff assembly and being as defined in one or more of the appended claims and, as such, having the capability of being constructed to accomplish one or more of the following subsidiary objects.
It is an object of the present invention to provide a method and apparatus for controlling the tension of wire being pulled from a wire spool mounted on a bead wire letoff assembly.
It is still a further object of the present invention to provide an improved bead wire letoff assembly that can accurately control full reels of wire at a line speed above about 300 fpm [91.44 mpm].
It is a yet further object of the present invention to provide an improved bead wire letoff assembly that incorporates a cam operated in accordance with the location of a tension arm to control air pressure to an air brake that applies a braking force to a spool.
Accordingly, there is disclosed a bead wire let-off assembly into which is mounted include a rotating wire spool having bead wire unwound therefrom. A brake system for applying a braking pressure to the spool is provided with a pressure regulator controlling the braking pressure applied by the brake system. A tension responsive control arm engages the bead wire and moves in response to changes in bead wire tension. The control arm is operationally connected to the pressure regulator so that the braking pressure applied by the brake system to the wire spool is a function of the position of the control arm.
According to the invention, the brake system has a first axle secured to and extending outward from the rotating wire spool, the first axle having a first centerline therethrough about which the spool rotates. A first gear wheel is attached to the first axle and a second axle being disposed in parallel relation to the first axle has a second gear wheel secured in engaging relationship with the first gear wheel. A pressure activated brake mechanism is provided to applying a braking force to the second axle in response to the receipt of pressurized air from the pressure regulator.
Further according to the invention, a third axle is disposed in parallel relationship to the first and second axles. The third axle has the tension responsive control arm and a cam plate secured thereto whereby movement of the control arm causes rotational movement of the cam plate. The pressure regulator has a piston rod engaging a cam surface of the cam plate whereby rotational movement of the cam plate causes an actuator piston rod to regulate the air pressure delivered from the pressure regulator to the air pressure brake. A bias force application device applies a biased force to urge the tension responsive control arm towards a position where the brake force is fully applied.
Also according to the invention, the method of controlling the unwinding of bead wire from a rotating spool includes the steps of: applying a braking pressure to the rotating spool with a brake system; regulating the braking pressure applied by the brake system with a pressure regulator; and controlling the braking pressure applied by the brake system as a function of the position of a tension responsive control arm engaging the bead wire and pivotably moving in response to a change in tension of the bead wire.
The method further includes the steps of: applying the braking pressure with a pressure activated brake mechanism that receives pressurized air from the pressure regulator to control the braking pressure applied by the brake system; pivoting the tension responsive control arm and a cam plate secured to cause rotational movement of the cam plate; engaging a cam surface of the cam plate with a piston rod extending from the pressure regulator whereby rotational movement of the cam plate causes an actuator piston rod to regulate the air pressure delivered from the pressure regulator to the pressure brake; and applying a force to urge the tension responsive control arm towards a position where the brake force is fully applied.